This invention relates to a diagnosis apparatus for diagnosing trouble occurring in any of the electronic control devices mounted on a vehicle, and for implementing control systems for controlled objectives, such as an engine control system and a transmission control system.
Many types of control systems mounted on a vehicle, for controlling the operation of the vehicle, employ electronics. These control systems include, for example, a system for electronically controlling the engine, systems for electronically controlling a transmission mechanism for transmitting engine power, and a system for electronically monitoring and controlling a braking operation. The control devices implementing these electronic control systems are individually provided and independently execute their control operations.
The control devices forming control systems are operated under their own controls. For example, when a problem occurs, these devices diagnose the problem independently. A simple element to detect the problem, for example, a sensor, performs the diagnosing function in each of the control devices.
In the above diagnostic system, a plurality of control devices are provided and independently execute the diagnostic operations, as described above. With this scheme, when the operation of one control system is abnormal, there are cases that the control system fails to identify its abnormal operation.